1. Field of the Invention
The subject invention generally pertains to flexible fabric air ducts and more specifically to a frame that supports the duct when it is deflated.
2. Description of Related Art
Ductwork is often used to convey conditioned air (e.g., heated, cooled, filtered, etc.) discharged from a fan and to distribute the air to a room or other areas within a building. Ducts are typically formed of rigid metal, such as steel, aluminum, or stainless steel. In many installations, ducts are hidden above suspended ceilings for convenience and aesthetics. But in warehouses, manufacturing plants and many other buildings, the ducts are suspended from the roof of the building and are thus exposed. In those warehouse or manufacturing environments where prevention of air-borne contamination of the inventory is critical, metal ducts can create problems.
For example, temperature variations in the building, or temperature differentials between the ducts and the air being conveyed can create condensation on both the interior and exterior of the ducts. The presence of condensed moisture on the interior of the duct may form mold or bacteria that the duct then passes onto the room or other areas being supplied with the conditioned air. In the case of exposed ducts, condensation on the exterior of the duct can drip onto the inventory or personnel below. The consequences of the dripping can range anywhere from a minor irritation to a dangerously slippery floor for the personnel, or complete destruction of the products it may drip on (especially in food-processing facilities).
Further, metal ducts with localized discharge registers have been known to create uncomfortable drafts and unbalanced localized heating or cooling within the building. In many food-processing facilities where the target temperature is 42 degrees Fahrenheit, a cold draft can be especially uncomfortable and possibly unhealthy.
Many of the above problems associated with metal ducts are overcome by the use of flexible fabric ducts, such as a DUCTSOX by the Frommelt Safety Products Corporation of Milwaukee, Wis. Such ducts typically have a flexible fabric wall (often porous) that inflates to a generally cylindrical shape by the pressure of the air being conveyed by the duct. Fabric ducts seem to inhibit the formation of condensation on its exterior wall, possibly due to the fabric having a lower thermal conductivity than that of metal ducts. In addition, the fabric's porosity and/or additional holes distributed along the length of the fabric duct broadly and evenly disperse the air into the room being conditioned or ventilated. The even distribution of airflow also effectively ventilates the walls of the duct itself, thereby further inhibiting the formation of mold and bacteria.
However, in many cases, once the room's conditioning demand has been met, the air supply fan is turned off until needed again. When the fan is off, the resulting loss of air pressure in the duct deflates the fabric tube: causing it to sag. Depending on the application and material of the fabric, in some cases, the sagging creates a poor appearance or may interfere with whatever might be directly beneath the duct.